U.S. patent number 5,654,786 [Application Number 08/584,567] was granted by the patent office on 1997-08-05 for optical lens structure and control system for maintaining a selected constant level of transmitted light at a wearer's eyes.
This patent grant is currently assigned to Robert C. Burlingame. Invention is credited to E. Gerald Bylander.
United States Patent |
5,654,786 |
Bylander |
August 5, 1997 |
Optical lens structure and control system for maintaining a
selected constant level of transmitted light at a wearer's eyes
Abstract
A lens structure and electronic control system is provided for
use in eyeglasses. The lens structure is formed by a pair of lenses
with a transmission layer formed by an electro-optic material is
disposed therebetween. The transmission layer is used to control
the amount of light that is transmitted through the lens structure
by placement of a variable voltage placed across it. The
transmission layer can be formed by either a dichroic dye or by a
ferro-electric material such as PLZT. The electronic control system
uses a photoamperic sensor placed behind the lens structure to
develop a current proportional to the transmitted light. The
current is converted into a voltage which is compared to a desired
transmission range. If the sensed transmission level is outside the
desired range the control circuit causes a power supply to add or
decrease the charge across the lens as necessary to bring the
transmitted light level back into the desired range. The use of a
ferro-electric material also requires the use of a high voltage
power supply to provide the necessary voltages to operate the lens
structure.
Inventors: |
Bylander; E. Gerald (Sherman,
TX) |
Assignee: |
Burlingame; Robert C. (Sherman,
TX)
|
Family
ID: |
24337876 |
Appl.
No.: |
08/584,567 |
Filed: |
January 11, 1996 |
Current U.S.
Class: |
351/49; 351/158;
351/41 |
Current CPC
Class: |
A61F
9/023 (20130101); G02C 7/101 (20130101); G02C
7/12 (20130101); G02F 1/0551 (20130101) |
Current International
Class: |
A61F
9/02 (20060101); G02F 1/055 (20060101); G02F
1/01 (20060101); G02C 7/10 (20060101); G02C
7/00 (20060101); G02C 007/12 (); G02C 001/00 () |
Field of
Search: |
;351/49,158,41,44,45,46
;359/62,63 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dang; Hung X.
Attorney, Agent or Firm: Harris, Tucker & Hardin,
P.C.
Claims
What is claimed is:
1. An optical device to be worn by a user comprising:
a) a lens structure having an optical transmissivity which is
electrically controllable, the lens structure including a pair of
lenses having a transmission layer therebetween, the transmission
layer being responsive to a variable voltage applied thereto for
varying an amount of light transmitted through the lens
structure;
b) a frame coupled to the lens structure, wherein the frame places
the lens structure in optical relationship with the user's
eyes;
c) a sensor mounted behind the lens structure to measure the amount
of transmitted light passing through the lens structure; and
d) a control circuit electrically coupled to the lens structure and
the sensor, and including a power source, the control circuit
sensing and responding to the amount of light transmitted through
the lens structure as measured by the sensor and electronically
adjusting the optical transmissivity of the lens structure by
varying the variable voltage applied to the transmission layer such
that the amount of light transmitted through the lens remains
within a predetermined range.
2. The optical device of claim 1 further comprising a second lens
structure, the frame being configured to place the lens structure
and the second lens structure in relationship to the user's
respective eyes.
3. The optical device of claim 1 wherein the transmission layer is
a ferro-electric material and the pair of lenses are each
polarizing lenses.
4. The optical device of claim 1 wherein the ferro-electric
material is composed of a lead-lanthanum zirconate/titanate
(PLZT).
5. The optical device of claim 1 wherein the transmission layer is
a dichroic dye sealed between the pair of lenses.
6. An optical device for controlling an amount of light received at
a wearer's eye, the optical device comprising:
a) a frame;
b) a lens structure mounted in the frame, the lens structure
including;
i) a first lens;
ii) a second lens;
iii) a transmission layer disposed between the first lens and the
second lens, the transmission layer having a electro-optic property
in response to and in proportion to an electric field placed across
the transmission layer such that the transmission layer determines
the amount of light that passes through the lens structure; and
iv) electrical terminals electrically connected across the
transmission layer to produce an electric field across the
transmission layer;
c) a sensor mounted behind the second lens to develop a signal
proportional to the light passing through the lens structure;
d) a control circuit electrically connected to the sensor, the
control circuit comparing the signal to a maximum transmission
level and a minimum transmission level to ensure that the light
passing through the lens structure is within a desired range;
and
e) a power supply electrically connected to the electrical
terminals and controlled by the control circuit, the power supply
used to add and remove charge from the lens structure in response
to the control circuit.
7. The optical device of claim 6 wherein the first lens and the
second lens are polarizing lenses, the first lens used to polarized
incident light into a transmission plane, and wherein the
transmission layer is a ferro-electric material which continuously
rotates the transmission plane in an amount proportional to the
electric field such that a percentage of the transmission plane is
absorbed by the second lens, the percentage corresponding to the
amount of rotation.
8. The optical device of claim 7 wherein the power supply is a high
voltage power supply capable of placing a voltage across the
electrical terminals of at least 500 volts.
9. The optical device of claim 7 wherein the ferro-electric
material is composed of a lead-lanthanum zirconate/titanate
(PLZT).
10. The optical device of claim 6 wherein the transmission layer is
a dichroic dye sealed between the first lens and the second lens,
the dichroic dye increasing transmissivity in response to the
electric field.
11. The optical device of claim 6 wherein the control circuit and
the power supply are mounted in the frame.
12. An optical device for controlling an amount of light received
at a wearer's eye, the optical device comprising:
a) a frame;
b) a lens structure mounted in the frame, the lens structure
including;
i) a first polarizer having a first plane of polarization to
receive light incident on the optical device and to transmit
polarized light, the polarized light being polarized in the first
plane of polarization;
ii) a transmission layer adjacent the first polarizer to receive
the polarized light, the transmission layer having an electro-optic
property such that the transmission layer rotates the polarized
light in response to and in an amount proportional to an electrical
field placed across the transmission layer;
iii) a second polarizer adjacent the transmission layer opposite
the first polarizer and having a second plane of polarization, the
second polarizer to receive the polarized light rotated by the
transmission layer and to transmit a percentage of the polarized
light, the percentage corresponding to the amount of rotation and
the second plane of polarization; and
iv) electrical terminals connected to the transmission layer, the
electrical terminals capable of holding a charge, the charge
inducing the electric field across the transmission layer;
c) a sensor mounted on the second lens opposite the transmission
layer, the sensor generating a signal proportional to the
percentage of polarized light transmitted by the second
polarizer;
d) a high voltage power supply and electrically connected to the
electrical terminals, the high voltage power supply used to control
the charge on the electrical terminals by placing a voltage across
the electrical terminals, wherein the voltage is continuously
variable up to a maximum safe voltage; and
e) a control circuit and electrically connected to the sensor and
the high voltage power supply, the control circuit receiving the
signal from the sensor and causing the high voltage power supply to
add or remove charge as necessary when the signal from the sensor
is outside a desired operating range.
13. The optical device of claim 12 wherein the transmission layer
material is composed of a lead-lanthanum zirconate/titanate
(PLZT).
14. The optical device of claim 12 wherein the first plane of
polarization and the second plane of polarization are in an
identical orientation such that the lens structure is transparent
when the electric field across the transmission layer is zero.
15. The optical device of claim 12 wherein the first plane of
polarization is perpendicular to the second plane of polarization
such that the lens structure is opaque when the electric field
across the transmission layer is zero.
16. The optical device of claim 12 wherein the frame includes a
seal extending from the frame to a forehead of the wearer and a
first and second earpieces, the seal and the first and second
earpieces providing a barrier to prevent ambient light from
reaching the sensor.
17. The optical device of claim 12 wherein the sensor is a
photoamperic sensor configured to generate a current when exposed
to a light source.
18. The optical device of claim 17 wherein the photoamperic sensor
is a gallium arsenide phosphide light emitting diode which
generates the current in response to light in essentially a visible
spectrum.
19. The optical device of claim 12 wherein the high voltage power
supply and the control circuit are mounted in the frame.
20. An optical device for maintaining a preset transmission level
of light at a wearer's eye, the eyewear apparatus comprising:
a) a frame including a left earpiece and a right earpiece and a
seal, the left earpiece, the right earpiece and the seal preventing
light from reaching the wearer's eye other than through the eyewear
apparatus;
b) a lens structure mounted in the frame and including a first and
second lens, each of the first and second lenses formed by
i) a first polarizer mounted in frame and having a first plane of
polarization, wherein the first polarizer receives ambient light
and transmits polarized light;
ii) a lead-lanthanum zirconate/titanate (PLZT) layer mounted in the
frame adjacent the first polarizer, the (PLZT) layer including a
plurality of filaments such that an electric field is developed
across the (PLZT) layer when a voltage is applied to the plurality
of filaments, wherein the (PLZT) layer receives the polarized
light, rotates the polarized light in an amount proportional to the
electric field, and transmits rotated polarized light;
iii) a second polarizer mounted in the frame adjacent to the (PLZT)
layer opposite the first polarizer, the second polarizer having a
second plane of polarization, wherein the second polarizer receives
the rotated polarized light from the (PLZT) layer and transmits the
preset light level to the wearer's eye; and
iv) electrical terminals electrically connected to the plurality of
filaments;
c) a sensor mounted on the second polarizer of the first lens,
wherein the sensor develops a signal proportional to the preset
light level transmitted by the second polarizer of the first
lens;
d) a high voltage power supply mounted in the frame and
electrically connected to the electrical terminals, wherein the
high voltage power supply supplies a continuously variable voltage
to the electrical terminals and a maximum safe voltage of at least
500 volts;
e) a control circuit mounted in the frame, the control circuit
being electrically connected to the sensor and the high voltage
power supply, wherein the control circuit causes the high voltage
power supply to alter the continuously variable voltage across the
electrical terminals in response to the signal from the sensor
corresponding to the preset light level having strayed outside a
preset transmission range.
21. The optical device of claim 20 wherein the first plane of
polarization and the second plane of polarization are in an
identical orientation such that the lens structure is transparent
when the electric field across the transmission layer is zero.
22. The optical device of claim 20 wherein the first plane of
polarization is perpendicular to the second plane of polarization
such that the lens structure is opaque when the electric field
across the transmission layer is zero.
23. The optical device of claim 20 wherein the sensor is a light
emitting diode configured to generate a current when exposed to a
light source.
24. The optical device of claim 20 wherein the light emitting diode
is a Gallium Arsenide Phosphide diode which generates the current
in response to light in essentially a visible spectrum.
Description
FIELD OF THE INVENTION
The present invention relates to lens structures which have an
optical transmissivity that can be electronically controlled, and
more specifically where the optical transmissivity is maintained at
or within a preset level. The present invention also relates to
eyewear incorporating an electronically controlled lens
structure.
BACKGROUND OF THE INVENTION
The are many instances when it is desirable or necessary to control
the amount of light passing through lens or lens structure. One of
these instances relates to the lenses used in eyewear. Continuous
control of optical transmissivity across a broad range of
magnitudes is particularly desirable in many medical applications
such as diagnosis and treatment of retinal disease, visual field
abnormalities known a scotomas, optic neuropathy, macular
degeneration, and the like. Diagnosis of these conditions can be
problematic using uncontrolled ambient light since the magnitude of
the symptoms of these diseases can vary with ambient light
levels.
For patients suffering from retinal diseases, sudden changes in
ambient light levels, such as emerging from a dimly lit room into a
bright sunny day, and vise versa, can cause serious problems and
momentary blindness. It would be desirable to maintain these
patients in a partially dark adapted state. This partially dark
adapted state would involve maintaining a constant light level at
the patients eyes despite variations in ambient light levels.
Existing devices for controlling optical transmissivity are not
suited for the applications described. Many of these devices cannot
continuously control transmissivity over a broad range of ambient
light levels. An example of this type of device is a flash
blindness device that darkens only when a sudden change in ambient
light levels is detected. One such device is disclosed in U.S. Pat.
No. 3,245,315 to Marks et al.
Other devices that control optical transmissivity have their
transmissivity dependent on ambient light levels. These devices
locate their sensors to detect the ambient light levels and not the
transmitted light levels. Transmitted light through these devices
is not constant and is dependant on the ambient light levels.
Ideally, for the applications described, transmitted light should
be independent of ambient light levels and constant within a narrow
range. Examples of devices with transmitted light levels dependant
on ambient light levels are U.S. Pat. No. 5,015,086 to Okaue et al.
and U.S. Pat. No. 4,968,127 to Russell et al.
What is needed is a device to continuously control optical
transmissivity over a broad range wherein the transmitted light is
independent of ambient light levels.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to provide a lens
structure and control system for eyewear that provides a high
degree of control over the amount of light passing through the
lens.
It is another object of the invention to provide a lens structure
for eyewear where the optical transmissivity is continuously
controllable over a broad range of transmission levels.
It is yet another object of the invention to provide a lens
structure for eyewear where the transmitted light level is
independent of ambient light levels.
It is another object of the invention to provide a lens structure
that changes optical transmissivity in response to a change in
ambient light levels faster than the recognition level of the
wearer.
In one embodiment of the invention the lens structure is comprised
of a transmission layer which is a ferro-electric material,
preferably PLZT, but can be lithium niobate or tantalate. The
transmission layer is placed between two polarizing lenses. A high
voltage power supply is used to develop a voltage across the
transmission layer which rotates the plane of polarization of the
light passing through it in an amount relative to the voltage
across the PLZT. This structure controls the amount of light
passing through the lens structure by controlling how much light is
passed by the second polarizer.
For example, if the two polarizers are aligned with the planes of
polarization at right angles to each other almost no light would
normally be allowed to pass through the lens structure. However, if
a particular large voltage is developed across the transmission
layer the polarized light passing through the first polarizer is
rotated, for example, 90.degree. such that it lies in the same
plane as the second polarizer and would pass undiminished through
the second polarizer. A lesser voltage across the transmission
layer would rotate the polarized light less than 90.degree. causing
less than total amount of light passed through the first polarizer
to pass through the second polarizer.
The amount of light passing through the lens is controlled by a
control circuit that begins with a sensor that measures the amount
of light passing through the lens and develops a current
proportional to that amount of light. The current is converted to a
voltage and sent to a window comparator configuration where the
sensed voltage level is compared to an upper threshold and a lower
threshold. If the sensed voltage is between the two thresholds the
control circuit takes no action. However, if the sensed voltage is
below the lower threshold or above the upper threshold the control
circuit turns on the high voltage power supply to increase the
voltage across the transmission layer or shorts the transmission
layer electrodes together to bleed off charge, respectively.
In an alternate embodiment the PLZT and dual polarizer structure is
replaced by a transmission layer formed by liquid dichroic dye
between two lenses one of which can incorporate a polarizer if the
application warrants. The dichroic dye lightens, or increases the
amount of light passing through it, in response to a voltage
developed across the dye. The dichroic dye lens structure can be
controlled by the control circuit described above except that the
dichroic dye does not require the very high voltages required by
the PLZT lens structure.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and features of the invention will become more
readily apparent from the following detailed description when read
in conjunction with the accompanying drawings, wherein:
FIG. 1 is a frontal view of eye glasses incorporating the lens
structure and electrical control system of the present
invention;
FIG. 2 is a rear view of the eye glasses shown in FIG. 1;
FIG. 3 is a side view of the eye glasses shown in FIG. 1;
FIG. 4 is a side view of the ferro-electric lens structure;
FIG. 5 is a frontal view of the ferro electric material;
FIG. 6 is a schematic diagram of the preferred embodiment of the
control circuit;
FIG. 7 is a schematic diagram of the preferred embodiment of the
high voltage power supply;
FIG. 8 is a schematic diagram of an alternate embodiment of the
high voltage power supply;
FIG. 9 is a schematic diagram of the preferred embodiment of the
low voltage power supply;
DETAILED DESCRIPTION
FIG. 1, 2 and 3 show eyewear 10 incorporating the invention. FIG. 1
is a frontal view of eyewear 10 which includes lenses 12 and 14
mounted in frame 16. Lenses 12 and 14 shown in FIG. 1 are
individually formed by two lenses with transmission layer formed by
a liquid dichroic dye sealed in between. Dichroic dye, as
configured in the present invention, responds by lightening when in
the presence of an electric field. The amount of the increase in
transmissivity by the dichroic dye is proportional to the amount of
electric field allowing the invention to continuously vary the
optical transmissivity of the lens in response to varying ambient
light conditions. The electric field is developed across the
transmission layer of dichroic dye by opposing electrodes formed by
continuous layers of indium tin oxide film which coat the interior
surfaces of the two lenses. The layers of indium tin oxide are
transparent and connected to opposite poles of a power supply to be
described with reference to FIG. 9.
FIG. 2 is a rear view of eyewear 10 and shows ear pieces 18 and 20
held to frame 16 by hinges 22 and 24. Hinges 22 and 24 allow ear
pieces 18 and 20 to fold in toward frame 16 for storage of eyewear
10, as is known in the art. Also shown is sensor 30 which is
mounted to the rear of lens 14 and measures the amount of light
that passes through lens. Sensor 30 is a photovoltaic detector and
produces a current proportional to the amount of light detected.
The preferred embodiment of the invention uses a Gallium Arsenide
Phosphide (GaAsP) green or red light emitting diode (LED) connected
as a photoamperic cell to function as sensor 30. The photoamperic
cell is connected to lens 14 using a transparent non-yellowing and
stress free epoxy such as Tra-Bond brand epoxy from Tra-Con of
Medford, Mass. A silicon photoamperic cell can be used with the
dichroic dye and non-polarizing lenses, but GaAsP is preferred for
the PLZT and dichroic dye using polarizers due to its lack of
detection in the infra-red spectrum. Detection by sensor 30 of
light outside the visible spectrum can cause serious discrepancies
between the sensed light level and the actual visible light level
and should be avoided.
Additionally, care must be taken to prevent light from reaching
sensor 30 from any direction other than through lens 14. To this
end, eyewear 10 includes seal 26 attached to the top of frame 16.
Seal 26 is formed from a pliant material such as foam rubber or a
thin plastic membrane and extends from frame 16 to the forehead of
the wearer preventing light from reaching sensor 30 through the
space between frame 16 and the wearer.
FIG. 3 shows a side view of eyewear 10. Ear piece 18 is formed to
prevent light from reaching sensor 30 from the side of eyewear 10
for the same reason as seal 26. Ear piece 18 includes peripheral
lens 32 which is polarized to restrict the amount of light that can
enter peripheral lens 32. Peripheral lens is included to allow the
wearer peripheral vision which is critical in applications such as
driving. The electronic control circuitry and power supply
circuitry are housed in ear pieces 18 and 20. Wiring connections 34
show the wiring of the circuitry discussed with reference to FIGS.
6 to 9.
Dial 36 allows the user to set the desired transmission level by
controlling resistor 116 from FIG. 6 and can act as an on/off
switch. An alternate on/off switch can be mounted in earpiece 18
such that when ear piece 18 is folded out from the storage position
using hinge 22 contact by ear piece 18 to frame 16 activates the
switch turning on the electronics of the invention. Additionally,
eyewear 10 is shown in FIG. 3 with neckstrap 38. Neckstrap 38 can
be configured to house lithium cell 264 from FIG. 9 in cell housing
40. Without neckstrap 38 the lithium cell for the electronics can
be housed in ear piece 18.
FIG. 4 shows another embodiment of lenses 12 and 14. Lens structure
50 is formed by polarizers 52 and 54 separated by a ferro-electric
material 56 which is preferably a lead-lanthanum zirconate/titanate
of the quaternary (Pb.sub.1-x La.sub.x)(Zr.sub.y
Ti.sub.z).sub.1-x/4 O.sub.3, system, commonly known as PLZT. PLZT
rotates the plane of polarization of an electro-magnetic wave
passing through it in response to an electric field. The amount of
rotation of the electro-magnetic wave is proportional to the
magnitude of the electrical field placed on the PLZT.
Lens structure 50 uses polarizer 52 to polarize the light entering
ferro-electric material 56 and the second polarizer, referred to as
analyzer 54 to polarize the light exiling ferro-electric material
56. An electric field is induced in ferro-electric material 56 such
that the light passed by polarizer 52 is rotated by ferro-electric
material 56 and a percentage of the remaining light is absorbed by
analyzer 54. Since the amount of rotation is proportional to the
electric field the amount of light passing through lens structure
can be controlled by controlling the electric field.
Polarizer 52 and analyzer 54 of lens structure 50 can be oriented
in two ways. By orienting the polarizers in the same plane the lens
structure is transparent when no electric field is applied to
ferro-electric material 56. One advantage of this arrangement is
that it is transparent if the power supply or control circuit fail.
Alternatively, if polarizer 52 and analyzer 54 are oriented
perpendicularly, the lens structure is opaque when no electric
field is applied to ferro-electric material 56.
FIG. 5 is a frontal view of ferro-electric material 56 used in the
present invention. The PLZT used as ferro-electric material 56 in
the preferred embodiment is not capable of developing a suitable
electric field across the entire lens. As a result ferro-electric
material 56 is constructed with small filaments 58 on surface 59 of
ferro-electric material extending in alternating succession from
either side of ferro-electric material 56. Filaments 58 extending
into ferro-electric material 56 from opposite sides are given
opposite electrical charges by the power supply of the present
invention. Filaments 58 allow the electric field to be formed
between each of oppositely charged filaments 58. If filaments 58
are placed on both surface 59 and the opposing surface (not shown),
of ferro-electric material 56, an electric field can be formed
between oppositely charged filaments on opposing surfaces.
Filaments 58 are connected to the high voltage power supply using
electrical connections 60 and 62.
Since dichroic dye lenses 14 and 12 shown in FIG. 1 does not
require polarizers, it may have a range of transmissivity from 10
to 80%. In contrast, lens structure 50 of FIG. 4 by requiring
polarizers can have a transmissivity that normally ranges from 4 to
24%, but can be as great as 1.times.10.sup.-3 to 36%. If the
application requires, such as sunglasses for a fisherman where the
light reflected off the water is polarized in a single plane, a
polarizer can be added to the dichroic dye lens resulting in a
range of transmissivity from 4 to 32%.
FIG. 6 is a circuit diagram of control circuit 100, the preferred
embodiment of the control circuit for the present invention which
is configured to control perpendicularly oriented polarizers. The
control circuit can easily be adapted to accommodate parallel
polarizers by reversing the comparator wiring of window comparator
120 described below. Photo diode 102 acts as sensor 30 from FIG. 1.
Photo diode 102 is preferably made from gallium arsenide phosphide
(GaAsP) or silicon, but must be excited almost exclusively by light
in the visible spectrum. Photo diodes sensitive to infra-red light,
such as unfiltered silicon, can cause a serious degradation in
system performance since commercial visible polarizers are
ineffective in the infra-red. As described above, photo diode 102
is mounted behind the lens structure such that it measures only the
light passing through the lens.
Photo diode 102 is effectively short circuited by connecting to
op-amp 106 so that it generates a current proportional to the
incident light intensity that is then passed through connector 104
to op-amp 106 which, in conjunction with resistor 108 converts the
current developed by photo diode 102 to a voltage that can be used
by the rest of control circuit 100. Op-amp 110 is used with
resistors 112, 114 and variable resistor 116 to amplify the signal
from photo diode to a level relative to the desired light level and
the preset reference voltages.
Window comparator circuit 120 utilizes discrete comparators 122 and
124 to compare the signal representing the light received by the
sensor to a high reference voltage and a low reference voltage. The
lens structure, as discussed above with reference to FIGS. 4 and 5,
is opaque when there is no voltage developed across it and becomes
progressively more transparent as the voltage across the lens
structure is increased from the threshold until the lens reduces to
its desired transparency to maintain the transmitted light at the
predetermined level. Therefore, the high reference voltage is used
to determine when the correct amount of light is exceeded and to
activate the circuitry to drain charge from the lens, thereby
darkening the lens. Conversely, the low reference voltage is used
to determine when too little light is passing through the lens and
to activate the voltage supply used to increase the charge across
the lens adjusting the lens to more transparency until the preset
transmitted light level is again reached.
Both the high reference voltage and the low reference voltage are
generated by using the initial bandgap voltage of a series of
diodes because the voltage drop across diodes are consistently
stable despite variations in the system voltage. In the preferred
embodiment, the high reference voltage is determined by the voltage
drop across diodes 126, 128, and 130 while the low reference
voltage is determined by the voltage drop across diodes 132, 134,
and 136. The high reference voltage and the low reference voltage
are in the range of 1.401 volts and 1.219 volts, respectively.
Resistor 138 is used to control the current through diodes 126,
128, and 130 while resistor 140 performs the same function with
diodes 132, 134, and 136.
Comparator 122 compares the voltage developed from photo-diode 102
with the low reference voltage. The voltage developed from the
photo-diode is connected to minus terminal 122m of comparator 122
while the low reference voltage is connected to plus terminal 122p
of comparator 122. When the voltage developed from photo-diode 102
falls below the low reference voltage comparator 122 is turned on
and output 122o of comparator 122 becomes system voltage 90.
Transistor 142 is used to switch output 122o of comparator 122 and
provide a stable SHUTDOWN signal 96. SHUTDOWN signal 96 is used to
turn on the high voltage power supply, shown in FIG. 7, charging
the lens structure of FIG. 4.
Charging the lens structure makes the lens more transparent
resulting in photo-diode 102 sensing more light and thereby
developing a greater current resulting in a greater voltage across
op-amps 106 and 110. When the light sensed by photo-diode 102 is
within the proper range the voltage developed by photo-diode 102 in
conjunction with op-amps 106 and 110 is above the low reference
voltage resulting in SHUTDOWN signal 96 being pulled to system
voltage, thereby causing the high voltage power supply to be turned
off. Resistor 146 is a pulldown resistor for the comparator and
used to control the voltage at the base of transistor 142, while
resistor 148 is used to pull SHUTDOWN signal 96 to system voltage
90 until grounded by transistor 142, turning on the high voltage
power supply.
Comparator 124 of window comparator circuit 120, compares the
voltage developed from photo-diode 102 with the high reference
voltage. The voltage resulting from photo-diode 102 current is
again connected to minus terminal 124m of comparator 124 while the
high reference voltage is connected to plus terminal 124p of
comparator 124. When the voltage from photo-diode 102 rises above
the high reference voltage comparator 124 turns off causing CROWBAR
signal 98 to be pulled to ground. CROWBAR signal 98 is used to
drain charge from the lens structure thereby darkening the lens. As
above, darkening the lens causes less light to be received by
photo-diode 102 resulting in the voltage developed by photo-diode
102 and op-amps 106 and 108 to be lowered. When the light passing
through the lens and received by photo-diode 102 returns to the
desired range, the voltage developed by photo-diode 102 falls below
the high reference voltage causing comparator 124 to turn on and
CROWBAR signal 98 to be pulled to system voltage 90. When CROWBAR
signal 98 is high no charge is drained from the lens structure and
its transmissivity remains in the desired range.
Comparators 150 and op-amp 152 are used to ensure that the lens
structure cannot be charged past a preset maximum safe voltage
which in the preferred embodiment is 500 volts. A voltage signal
proportional to the lens voltage is sent to control circuit 100 via
connector 153. The development of the voltage signal will be
discussed in the description of FIG. 7. The voltage signal is fed
to op-amp 152 which is configured as a voltage follower. The output
of op-amp 152 is connected to comparator 150 through capacitor 154
and resistor 155 which provide a time delay, if so desired, between
the output of op-amp 152 and the input of comparator 150 dependant
on the resulting RC constant.
The voltage received from the high voltage power supply is compared
to the high reference voltage by comparator 150. When the voltage
received from the high voltage power supply is equivalent to a lens
voltage of the preset maximum safe voltage comparator 150 output
turns off, or is pulled to ground. This in turn causes the low
reference voltage to become grounded ensuring that the voltage
developed from photo-diode 102 is greater than the low reference
voltage. As discussed above, when the voltage developed from the
photo-diode is greater than the low reference voltage, comparator
122 is off or 0 volts and the output of transistor 142, which is
SHUTDOWN signal 96, is system voltage 90 causing the high voltage
power supply to be turned off. In this way, whenever the voltage
across the lens is at or above the preset maximum safe voltage
comparator 152 forces SHUTDOWN signal 96 to turn off the high
voltage power supply.
FIG. 7 is a circuit diagram of high voltage power supply 160, the
preferred embodiment of the high voltage power supply of the
present invention. High voltage power supply 160 can also be
referred to as a boost switching power supply. High voltage power
supply 160 begins with op-amp 162 which together with resistors
164, 166, 168 and 170 and capacitors 172 and 174 form pulse
generator 178. Pulse generator 178 produces an pulse output
determined by the time constant formed by resistor 164 and
capacitor 174. The output of op-amp 162 which is also the output of
pulse generator 178 is connected to the base of switching
transistor 180. Switching transistor 180 is used to control
inductor 182.
Switching transistor 180 when turned on by square wave generator
178 connects inductor 182 between positive power 91 and negative
power 93, both developed by the low voltage power supply shown in
FIG. 9, allowing inductor 182 to charge. When pulse generator 178
switches its output, switching transistor 180 is turned off and
inductor 182 is no longer connected to negative power 93, but
instead discharges the energy stored during the charging phase into
capacitors 186 and 188. Capacitors 186 and 188 are prevented from
discharging by diodes 190, and 192, and build up charge each time
inductor 182 discharges causing the voltage across the capacitors
to increase with each charging phase.
This charge forms a voltage across high voltage terminals 196 and
198, across which the lens structure is connected. The resulting
voltage across 196 and 198 is the sum of the voltage across
capacitors 186 and 188. For example, if the voltage built up across
capacitors 186 and 188 is 250 volts for each capacitor the voltage
seen across high voltage terminals 196 and 198 and therefore the
lens structure is 500 volts.
Resistors 200 and 202 form a voltage divider in parallel with high
voltage terminals 196 and 198. The voltage drop across resistor 202
is proportional to the voltage across the lens structure and forms
the feedback voltage sent from the high voltage power supply to
control circuit 100 of FIG. 6 through connector 153.
Transistor 204 and resistor 206 form the mechanism by which charge
is drained primarily from the PLZT lens, thereby reducing the
voltage across the high voltage terminals. Base 204b of transistor
204 is connected to CROWBAR signal 98 from control circuit 100 of
FIG. 6. When CROWBAR signal 98 is at system voltage 90, transistor
204 is turned on and provides a connection between capacitors 186
and 188 and ground allowing capacitors 186 and 188 to discharge
until CROWBAR signal 98 is switched from system voltage 90 to
ground.
FIG. 8 is a circuit diagram of a circuit implementing an alternate
embodiment of the high voltage power supply. Alternate high voltage
power supply 210 utilizes a self-oscillating transformer circuit
212 to charge capacitors 216, 218, 220, and 222. Self-oscillating
transformer circuit 212 is formed by transformer 214 which is
controlled by transistor 224. Transistor 224 has its base 224b
connected to feedback capacitor 226, feedback resistor 228, and
variable resistor 230 which are used to control the switching of
transistor 224 and the output of self-oscillating transformer
circuit 212 by the setting of the value of variable resistor
230.
Self-oscillating transformer circuit 212 charges capacitors 216 and
218 when current flows through transformer 214 in one direction and
charges capacitors 220 and 222 when current flows through
transformer 214 in the opposite direction. Capacitors 216, 218,
220, and 222 are prevented from discharging by diodes 232, 234,
236, and 238 and, therefore, build-up voltage in the same manner as
described above in the preferred high voltage power supply of FIG.
7. High voltage terminals 240 and 242 are connected to electrical
connection 60 and 62 of the lens structure shown in FIG. 5 and
represent the sum of voltages across all four capacitors 216, 218,
220, and 222. The use of four capacitors requires that each only
need charge to a value of 125 volts in order for 500 volts to
appear at high voltage terminals 240 and 242. The disadvantage of
this circuit is that transformer 224 is quite large, whereas
inductor 182 of FIG. 7 is comparatively small, on the order of 0.1
inches in diameter.
CROWBAR signal 98 utilizes transistor 246 to drain charge from the
lens structure, by turning on transistor 246 and providing a path
for capacitors 216, 218, 220, and 222 to discharge whenever CROWBAR
signal 98 is made high, or system voltage 90 by control circuit 100
shown in FIG. 6. Additionally, resistors 248 and 250 form a voltage
divider in parallel with high voltage terminals 240 and 242. The
voltage drop across resistor 250 is proportional to the voltage
across the lens structure and forms the feedback voltage sent from
the high voltage power supply to control circuit 100 of FIG. 6
through connector 153.
FIG. 9 is a circuit diagram of the preferred embodiment of the low
voltage power supply. Low voltage power supply 260 is used to
provide system voltage 90 as well as positive power 90 and negative
power 92 which are used to power the high voltage power supply of
either FIG. 7 or FIG. 8. Low voltage power supply uses voltage
regulator 262, which is preferably a Maxim MAX772 voltage
regulator, to regulate the voltage provided by lithium 264 and
supply a stable positive power 91 and negative power 93. System
voltage 90 is drawn directly from lithium cell 264 so that control
circuit 100 is always powered. ON/OFF input 266 of voltage
regulator 262 is connected to SHUTDOWN signal 96 from control
circuit 100 of FIG. 6. This connection allows control circuit 100
to connect and disconnect power to the high voltage power supply by
turning on and off voltage regulator 262. By this manner, SHUTDOWN
signal 96 is used to activate the high voltage power supply to
charge the lens structure as described with reference to FIG.
6.
Low voltage power supply 260 can be used without a high voltage
power supply to provide the required voltage in a dichroic dye lens
structure as described with reference to FIG. 1. The dichroic dye
lens structure only requires in the range of 18 volts maximum. This
level of voltage can be developed using only voltage regulator 260.
The voltage at positive power 91 and negative power 93 is
controlled by resistor R.sub.x 268 and R.sub.y 270 according to the
relationship V=((R.sub.x -R.sub.y)/R.sub.y)1.5. With positive power
91 and negative power 93 terminals connected across the lens
structure, control circuit 100 of FIG. 6 can be used with low
voltage power supply 260 to control the transmissivity of eyewear
10 from FIG. 1.
The preferred embodiment of control circuit 100 shown in FIG. 6
utilizes the following parts and component values:
______________________________________ Drawing No. Type Part No.
Manufacturer ______________________________________ 142 Transistor
ZRA1250FOCT Zetech 122, 124, 150 Comparator LP339
Natl.Semiconductor 152 Op-Amp LP324 Natl.Semiconductor 125, 130,
134, Diode BAU99 Zetech 136 126, 132 Diode IN914
______________________________________
The preferred embodiment of high voltage power supply circuit 160
shown in FIG. 7 utilizes the following parts and component
values:
______________________________________ Drawing No. Type Part No.
Manufacturer ______________________________________ 162 Op-Amp Max
474 Maxim 180, 204 Transistor MTD2N50E Motorola 182 Inductor
78F102J J. W. Miller 190, 192 Diode IN4927 194 Diode IN914
______________________________________
The preferred embodiment of high voltage power supply circuit 210
shown in FIG. 8 utilizes the following parts and component
values:
______________________________________ Drawing No. Type Part No.
Manufacturer ______________________________________ 214 Transformer
F073 Micro Trans 224 Transistor FMMT5551 Zetech 244 Transistor
ZRA1250 Zetech 246 Transistor MTD1N60E Motorola 232, 234, 236, 278
Diode IN4937 ______________________________________
The above listed parts and components can be obtained from various
electrical parts manufacturers. Specifically, general components
and Zetech, Plessey and Phillips parts can be obtained from
Digi-Key Corp., Thief River Falls, Minn. National Semiconductor
components can be obtained from National Semiconductor, Santa
Clara, Calif. J. W. Miller component can be obtained from the J. W.
Miller Division of Bell Industries, Gardens, Calif. Maxim
components can be obtained from Maxim Integrated Products,
Sunnyvale, Calif. Motorola components can be obtained from
Motorola, Inc., Schaumburg, Ill. The MicroTrans transistor can be
obtained from MicroTrans, Inc., Valley Stream, N.Y., and the PLZT
lenses can be obtained from Aura Systems, Inc., El Segundo, Calif.
Finally, the lithium cell is preferably a Tadiran TL5134 3.6 V cell
available from Newark Electronics, Chicago, Ill.
While the invention has been particularly shown and described with
reference to a preferred embodiment, it will be understood by those
skilled in the art that various changes in form and detail may be
made therein without departing from the spirit and scope of the
invention.
* * * * *